x/mobile: gobind ignores $GOROOT

[nikolay-turpitko]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.7.3 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/nick/go"
GORACE=""
GOROOT="/home/nick/.local/share/umake/go/go-lang"
GOTOOLDIR="/home/nick/.local/share/umake/go/go-lang/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build692640341=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

go get golang.org/x/mobile/cmd/gobind
export ANDROID_HOME=/home/nick/Android/Sdk/
cd $GOPATH/src/golang.org/x/mobile/example/reverse/android
gradle gomobileDebug --debug

What did you expect to see?

Successful build

What did you see instead?

Build error:

13:24:54.446 [ERROR] [system.err] 2016/12/06 13:24:54 failed to go install the generated Java wrappers: exit status 2: go: cannot find GOROOT directory: /usr/local/go
...
BUILD FAILED

My current workaround

diff --git a/cmd/gobind/gen.go b/cmd/gobind/gen.go
index 8325b84..2327721 100644
--- a/cmd/gobind/gen.go
+++ b/cmd/gobind/gen.go
@@ -178,7 +178,8 @@ func genJavaPackages(ctx *build.Context, dir string, classes []*java.Class) erro
                "-pkgdir="+filepath.Join(dir, "pkg", ctx.GOOS+"_"+ctx.GOARCH),
                "Java/...",
        )
-       cmd.Env = append(cmd.Env, "GOPATH="+dir)
+       //cmd.Env = append(cmd.Env, "GOPATH="+dir)
+       cmd.Env = append(os.Environ(), "GOPATH="+dir)
        if out, err := cmd.CombinedOutput(); err != nil {
                return fmt.Errorf("failed to go install the generated Java wrappers: %v: %s", err, string(out))
        }

Then go install golang.org/x/mobile/cmd/gobind.

[gopherbot]

CL https://golang.org/cl/46671 mentions this issue.